This work continues our studies on the immunogenetic factors influencing reproduction with particular emphasis on the role of the major histocompatibility complex. The major objectives are to investigate the genetic control of growth and reproduction and to explore the humoral and cellular immune responses to pregnancy. We have discovered a unique strain of rats (B1 strain) which has defects in growth and reproduction whose control is linked to the major histocompatibility complex. We plan to use this animal to: a) continue exploring the genetic control of these defects; b) investigate the interactions between these genes and the Y chromosome using lines congenic for both the MHC and the Y chromosome; c) define the anatomy of the gonadal defects in an attempt to correlate the anatomical defects with specific gene action; d) determine the cause of the decreased litter size of the B1 strain, and e) explore some potential molecular mechanisms underlying these defects. We wish to pursue our observation that the cellular immune response to pregnancy, as measured by MIF production, is apparently controlled by the A region of the MHC, whereas the immune responses to other foreign antigens are controlled by the B region. We also plan to explore systematically the antibody rsponse to pregnancy in order to define the types of immunoglobulin produced during pregnancy, their genetic control and their biological functions. The resources that we possess -- the mutant B1 strain, animals congenic for the MHC and the Y chromosome, a variety of congenic lines and a large colony of inbred rats -- provide us with a unique opportunity to study immunologic and genetic factors influencing growth and development and to study further the structure and function of the major histocompatibility complex in the rat which is the major theme of the work in our laboratory.